Opposed rotor radial piston pumps



July 10, 1962 R. J. POULlN 3,043,232

OPPOSED ROTOR RADIAL PISTON PUMPS Filed Jan. 22, 1958 2 Sheets-Sheet 1FM; Ilo

20 717 g? i 13 m W -10 l9 18@ t July 10, 1962 R. J. POULIN 3,04

OPPOSED ROTOR RADIAL PISTON PUMPS Filed Jan. 22, 1958 2 Sheets-Sheet 2 Il I 36 l 3 5 39 1 7/ IN VEN TOR 3,043,232 GPPQSED RGTGR RADKAL PISTGNPUMPS Raymond J. Poulin, R0. Box 808, Topanga, Cahfl, as-

signcr of one-half to Edward H. Rose, Santa Monica,

Calif. Filed Jan. 22, 1953, Ser. No. 710,523 14 Claims. (Cl. 103-161)This invention relates to radial piston pumps and, more particularly, toan opposed rotor radial piston pump in which the pistons in each rotorare depressed by engaging the surface of the other rotor, and which isadapted to provide high volume at medium pressures.

and high pressures at low volume and requiring less power for itsoperation than is needed for conventional pumps.

During their operating cycles many hydraulically powered machines suchas hydro presses, injection molding machines, and the like, require alarge volume of fluid at medium pressure to move certain parts of themachine from one position to another and additionally, for briefperiods, require peak pressures many times as great. In order to meetthese requirements engineers have found it necessary to select pumpshaving large volume output and power them with motors having suificienthorsepower to deliver the peak pressures required. This problem provesparticularly difficult in the case of constant volume pumps.

. Accordingly, the use of accumulators has become common in the generalart as a means for reducing the inordinately high power required inhydraulically operated machines of this type and, more recently,variable flow radial and axial piston pumps have served to furtherreduce the disproportionate ratio between the power required to fulfillperformance requirements. However, the plunger or piston type pumpsheretofore available have followed design patterns characterized byattendant problems such as the rugged construction required for highpressures and the somewhat complicated mechanisms involved in volumecontrol that left much to be desired in simplicity and operationalefficiency as well as in the operating power required.

My invention has been made with the foregoing considerations in mind,and can be said to have a plurality of important objectives.

One important object of my invention is the provision of a radial pistonpump being adapted to fulfill high volume and pressure requirements onminimal operating power. 1

Another important object of my invention is the provision of a radialpiston pump being adapted with opposed cylindrical rotors disposed intangential juxtaposition whereby each rotor serves as camming means fordepressing the radially disposed pistons of the other.

A further object of the present invention is the provision of a radialpiston pump of the character described being adapted to provide a widerange in volume output without the employment of substantiallycomplicated mechanical control means.

An additional object of my invention is the provision of a radial pumpof the character described and being adapted in conformation whereby theamount of time and movement devoted to the inlet phase of the pumpingcycle during each revolution of the rotors is several times as great asthat of the exhaust phase.

Another object of my invention is the provision of a radial piston pumpof the character described which is adapted with means for changing andcontrolling the ratio between its volume and pressure outputs.

A still further object of my invention is the provision of a radialpiston pump of the character described be- Patented .iuly 10, 1962 sitedrates Fatent @t tge WW2 2 ing adapted with piston actuation and fluidinlet control means being effective to substantially eliminate forcedleakage around the pistons together with the friction, noise and heatgenerated thereby.

In brief, the opposed rotor radial piston pump of my invention includesa pair of cylindrical rotors juxtaposed in coplanar alignment,journalled on parallel stationary shafts and intergeared-forcontrarotation. In each rotor is a plurality of radial bores fitted withpistons having dome-shaped heads which extend outwardly of thecircumferential periphery of the rotors, and the two rotors arerelatively positioned and intergeared so that the piston domes of eachare alternately depressed upon engagement with the periphery of theother as the rotors revolve.

The stationary shafts which in the present embodiment are conformed inthe manner of studs or pintles, are provided with inlet and exhaustducts which open laterally of the shafts in line with the rotor bores.The exhaust ducts open in the direction of the point of contact of thetwo rotors, and the inlet duct-s open oppositely into channels disposedcircumferentially of the shafts and terminated adjacent opposite sidesof the exhaust duct openings. A pressure sensitive flow valve,introduced in the fluid supply line, serves to control the amount offluid drawn into the bores from the inlet channels during the inletphase of each revolution. The

pistons are provided with return springs adapted to move the pistonsoutwardly in the bores only as far as necessary to draw in the availablefluid. Thus, reducing the inlet flow shortens the stroke of the pistonsand reduces the volume output of the pump without reducing the pres-suredeveloped or imposing a greater load on the motor. Interchangeability ofdriving gears permits additional latitude in the selection of power tomeet the general requirements of the machine being operated.

Other objects of my invention as well as possible variations in the formand details of the embodiment set forth will be apparent in thefollowing specification when it is examined together with the referencesmade therein to the accompanying drawings, of which:

EEGURE l is a frontal perspective view of an opposed rotor radial pistonpump constructed according to my invention;

FIGURE 2 is a sectional view taken along a horizontal plane through thefrontal gear housing disposed as seen in FIGURE 1 with the upper half ofthe gear housing removed to show the elements therein;

FIGURE 3 is a schematic diagram showing the manner in which the domedheads of the pistons are alternately engaged by the cylindricalperiphery of the other rotor and are pressed inwardly thereby;

FIGURE 4 is a schematic diagram, similar to that of FIGURE 3, in whichthe rotors are segmented to indicate the proportion of each revolutiondevoted to the exhaust and inlet phases of the pumping cycle; 7

FIGURE 5 is a perspective diagram of one of the identical stationaryshaft members showing the positions therein of the ducts directing fluidto and through the FIGURE-6 is a horizontal section taken along thelines and in the direction indicated by the arrows 6-6 in FIG- URE 5FIGURE 7 is a diagrammatic section taken verticaHy and axially of one ofthe ducted shafts such as the one shown in FIGURE 5;

FIGURE 8 is a vertical section of one rotor assembly taken axially ofthe shaft positioned as shown in FIG- URE 2, with the housing completelyremoved and the ducting, which is normally provided by the housingstructure, shown schematically, and

FIGURE 9 is a frontal view of a variation in the arrangement andconstruction structed according to my invention showing the manner inwhich they may be used and ducted in multiples in pumps of largercapacities. v 7

Reference is again made to FIGURE 1 in which a radial piston pumpconstructed according to my invention is designated generally by thenumeral 10 and is seen to include a motor 1 1, a motor fan and oilcooler assembly 12, attachment. means 13, and a forwardly disposed gearhousing 14 including two closure plates 15 and 16, and a frontallyextended area 17 disposed forwardly of the frontal surface 18 of theplate 15 in which the inlet and exhaust hydraulic lines 19 and 20respectively are received.

In the horizontal sectional view of FIGURE 2 the upper half of thehousing 14 has been removed to more clearly indicate the relativepositioning of the pump eleof the pump rotors con-' ments positionedtherein. The half sections 15 and 16 V of the housing 14 are securedtogether by suitable fastening means such asthe machine bolts 21 andremovably attached to the cooler assembly 12 by bolts such as shown at'22 in FIGURE 1.

The rotors 23 and 24 as shown in FIGURE 2 are formed integrally with thespur gears 25 and 26. The hollow member 28 which is diminishedindiameter at 29 to pro-.

vide a shaft section to which the spur gear 34) is aflixed.

The pinion gear 31 which is journalled on a stud 32 extending outwardlyfrom and integrally formed with the closure section 16, engages both thedrive shaft of the power source 11 and the spur gear 30. As will bereadily understood, changes in the ratios of the gears and 31 may bemade to alter the speed of rotation of the rotors 23-and 24. r g The tworotors 23 and 24 including their engaging gear sections 25 and 26 andtheir outwardly extended drive members 27 and 28, respectively, arejournalled on stationary shafts 33 and 34 which for the sake ofillustrative and descriptive clarity, have been indicated as separateshort shaft sections but are actually fixed to the structure and v inactual practice are formed integrally with the casing 4 vided with acircumferential shoulder as shown at from which a short shaft section 51is extended and terminated outwardly in a domed head 52. A retainingring 53, adapted to fit around the circumferential periphery of thepiston area of the rotor 23, is provided with perforations adapted toreceive slidably therein the shaft portions such as 51 and through whichthe pistons, such as 45, move outwardly until restrained by the shouldersections, as indicated at 50.

As shown in FIGURE 8 the piston 45 is seen to be at the limit of outwardmovement during the intake phase of the pumping cycle, and the piston46, opposite therefrom, is shown completely depressed inwardly of thecylindrical bore 44 by engagement of its domed head 54 against the outerperiphery of therotor 24, fluid being supplied to the bore 43 throughthe inlet duct 35, and exhausted inwardly of the piston46 through theexhaust duct 38. V

The means employed for controlling the volumeoutput of the pump is alsoshown schematically in FIGURE 8. From the exhaust duct 38 a lineindicated by the numeral 56 opens into a pressure sensitive flow valve57 having adjustment means'indicated by the knob 58 effective to reducethe inlet flow in the inlet duct 35 to any desired degree and adjustmentmeans calibrated in units of pressure indicated by the dial 59 forpresetting the pressure at which the flow restriction becomes operative.

The control system above described permits the pump to supply acomparatively large volume outputat mod erate pressures for the purposeof moving parts of a machine from one position to another as has beenpreviously explained, and then, as peak loads are approached, reducingthe flow of inlet fluid thereby shortening the stroke of the pistons,which move outwardly in the fluid tight cylinders only as far asrequired to accommodate the 7 available volume of inlet fluid, thusreducing the volume section 15 in the manner of projecting studs orpintles.

'Iheir conformation will be more clearly understood by reference to theperspective view and the horizontal and vertical sectional views of theshaft 33 shown in FIGURES V 5, 6 and 7'respectively. 1

The inlet duct which is designated generally by the numeral 35 inFIGURES 5-7 is entered through the bottom of the shaft as seen at 36 andopens laterally thereof into a semicircular channel 37 which is extendedcircumferentially of the shaft as best seen in the sectional 'view ofFIGURE 6 which is taken along the line and in the direction indicated bythe arrows 6-6 in FIGURE 5.

' a The exhaust duct 38 is entered through the side of the shaft 33 asshown at 39 in FIGURES 5 and 7, and is ex- 7 tended; upwardly and openedlaterally of the shaft at the aperture 40 which is disposed intermediateof the terminations 41 and 42 of the circumferential channel 37.

' Referenceis made to the vertical sectional view of FIG- URE 8 showingone of the rotor assemblies and the mannertin which the drive sleeve 27,radial piston rotor sec tion 23 and spur gear bottom portion 25 areintegrally formed in a single piece journalled on the stationary shaft33.

- Each of the'rotors 23 and 24 is provided with a plurality ofradial-bores such as 43 and 44 which are clearly shown in section inFIGURE 8.

a Each of the bores such as 43 and 44 is fitted with a piston, such as45 and 46,which includes a sleeve portion as'seen at 47 adapted toreceive one end of a spring 48; the opposite end of the spring 48 beingreceived and retained in a section 49 of the bore 43 of reduceddiameter.

outwardly of' the sleeve portion 47 the piston 45 is pro- 7 output andenabling the pressure to be substantially increased withoutoverburdem'ng the power supply.

The schematic diagram of FIGURE 3 clearly illustrates the manner inwhich the pistons of each rotor are alternatelydepressed upon engagementwith the circumferential surface of the other rotor, and furtherindicates the positions of the pistons in each of the rotors and thepositioning of the rotors relative to each other, and the alternatesequence of piston movement.

:In FIGURE 3 therotors 61 and 62 are shown schematically as they wouldappear when viewed in the direction of arrow 3 in FIGURE 2 with theclosure plate 16 removed, The shafts 63 and on which the rotors arejournalled are-shown cross sectionally along a plane being coincidentwith the axial centerlines of the radial bores, such as 43 and 44 inFIGURE 8, and of the circumferential inlet channel such as 37 in FIGURE6. The positions of certain of the pistons within the rotors areindicated inphantom. a 1 l With the rotors revolving oppositely in thedirections indicated by the arrows 65 and 66, the domed piston head v67of the rotor 61 is seen to be partially depressed as it engages thepiston retaining ring 62-R of the rotor 62, and the inner opening 68 ofthe radial bore 68 is partial communicating alignment with the exhaustaperture 70 of the stationary shaft 63; and simultaneously the piston 71isseen to bemoving outwardly of the rotor 61, and the opening 72 of theradial bore 73 is beginning to overlap the inlet channel 74 whichcommunicates with the inlet duct 75. Meanwhile the piston 76 in the bore77 of the rotor, 62 is seen to be completely depressed inwardly and theopening 78 of the bore 77 has rotated beyond the point of axialalignment with the opening 79 of the exhaust 'duct 80 in the stationaryshaft 64.

An understanding of the relatively short amount of time required forthe'exhaust phase compared to theinlet phase of the pumping cycle can beobtained from the purely schematic diagram in FIGURE 4 in which each ofthe rotors 81 and 82 is providedwith eight pistons in- '5 dicat'ed bythe domed heads '83 and 84 respectively, with the axial centerlines ofthe bores being indicated by the diametric lines such'as 85 and 86 witheach acute angle therebetween being of forty-five degrees. It isapparent, in the diagram, that the difference in the positions of thediametric line 87 in the rotor 81 and that of the line 88 in the rotor82 represents only 22 /2 degrees of rotation and, by reference also toFIGURE 3, that the majority of the actual discharge of fluid from thecylinder bore takes place within this span of movement. It is furtherapparent that if each rotor were supplied with twelve pistons, thediametric axial centerlines such as 85 and 36 would be spaced at thirtydegree angles, and the discharge of one piston would be completed duringeach fifteen de grees of rotation of the two rotors.

For production machines requiring greater volume or higher pressuresthan that available from a single pair of rotors having a given numberof pistons of given displacement such as has been previously described,my invention encompasses the use of a plurality of rotors as indicatedschematically in FIGURE 9 wherein two rotors 89 and 90 are superposedand rotate in contact with the rotors 91 and 92. Each pair of rotors isjournalled upon shafts such as that shown in vertical section at 93 inFIGURE 9. The inlet duct 94 is provided with a plurality of apertures asindicated at 95 and 96 which open into the circumferential inletchannels previously described, and the exhaust duct 97 is similarlyprovided with openings such as 98 and 99 which communicate with thepiston bores. A further variation of this duel rotor embodiment isindicated by the fragmentary section 100 in FIGURE 9 showing the twosets of piston bores disposed in a single cylindrical section, andexperiments conducted with test models indicate that the number ofpistons that can be used in this manner in longer cylindrical rotors islimited only by the difficulty encountered in ducting the fluid to andfrom the pistons.

The invention also anticipates and encompasses substantial variation inthe bore and stroke of the pistons and in the shape, length and generalconformation of the outwardly extended piston heads as compared to therelative sizes implied in the illustrations of the embodiment set forthherein.

For instance, very successful results were obtained from one testprototype in which shallow circular sockets such as 101 and 102 inFIGURE 9 were provided in the piston retaining rings between each pairof piston heads, and the pistons having generally half-round heads suchas that seen at 103 were replaced with pistons with ovularly conformedheads such as 104 and longer shaft sections as indicated at 105. Sincethe heads and sockets are complementary in conformation, each ovularhead is received in its respective socket and is pressed inwardly of itsbore with minimal lateral pressure as the longitudinal axes of the headsand sockets rotate into longitudinal alignment. This modification makespossible an increase in the piston stroke without measurable increase inpiston or cylinder wear.

From the foregoing specification and description it will be apparentthat the opposed rotor radial piston pump of 'my invention is adapted tooperate smoothly and quietly since its mechanical arrangement does notinvolve any violent eccentric movement characteristic of the wobbleplates, ofiset cylinders and eccentric rotation employed in conventionalpositive displacement piston type pumps.

It will also be observed that I have provided a greatly simplifiedpumping mechanism consisting of contrarotating circular cylinder blocks,each having a plurality of radial pistons therein and each serving ascamming means for depressing the cylinders of the other.

It willbe further observed that by employing this opposed rotorarrangement the friction producing factors have been substantiallyreduced and I have provided a pump adapted to remain cool and efiicientduring prolonged periods of operation.

I have also included means for increasing the duration of the inletphase of the pumping cycle compared to that of the exhaust phase, andhave provided a porting system which eliminates forced leakage of thefluid, a common characteristic in conventional piston type pumps.

Attention is also called to the fact that the opposed rotor radialpiston pump of my invention has been shown to provide wide variations involume output without the employment of substantially complicatedmechanical control means. 7 p

it is to be noted further that I have provided a radial piston pumpwhich is capable of fulfilling high volume and pressure requirements ona minimum of operating stricted to the embodiment set forth herein norlimited in any manner except as may be defined by the extent of theappended claims.

What I claim is:

1. A radial piston pump, comprising: a pair of cylindrical rotors havingspaced parallel planar surfaces and cylindrical peripheral sidewallstherebetween, and, each having a plurality of radial bores disposeduniformly therein and each of said rotors having a spur gear portionformed integrally therewith; pistons fitting slidably within said boresand being provided with rounded heads normally extended outwardly ofsaid cylindrical peripheral sidewalls of said rotors; said rotors beingjournalled on parallel shafts having fluid ducts therein, said ductsbeing apertured laterally of said shafts in axial alignment with saidradial bores; said rotors being disposed with their respective planarsurfaces in coplanar relationship and their cylindrical sidewallssubstantially in tangential contact between said shafts, and with theirspur gear portions in mating engagement and effective to counter-rotatesaid rotors and alternately depress the pistons of each of said rotorsinwardly of said bores as said outwardly extended piston heads rotateinto abutting contact with said cylindrical sidewall of the other rotor.

'2. A radial piston pump, comprising: a fluid tight housing; a pair ofstationary shafts disposed axially parallel interiorly of said housing,said shafts having fluid ducts therein; said ducts being aperturedlaterally of said shafts at one end and opening outwardly of saidhousing at the other end; a pair of cylindrical rotors journalled onsaid shafts, each of said rotors having a plurality of radial boresdisposed uniformly therein and opening inwardly alignment with saidapertures of said ducts; pistons fitting slidably within said bores andbeing provided with rounded heads normally extended outwardly of thecylindrical sidewalls of said rotors; said stationary shafts beingspaced apart so as to bring the cylindrical sidewalls of said rotors insubstantial contact tangentially along a line parallel to the axes ofsaid parallel shafts; said rotors having engaging spur gear portionsrespectively rigid therewith and effective to counter-rotate said rotorsso that the pistons of each of said rotors are alternately depressedinwardly of said bores upon coming into contact with said cylindricalsidewall of the other rotor, thereby discharging through one of saidducts fluid received in said bores from the other of said ducts.

3. In a radial piston pump, the combination comprising: a pair ofcylindrical rotors journalled on parallel shafts having fluid ductstherein and being spaced apart to bring the cylindrical sidewalls ofsaid rotors into substantial contact tangentially along'a line (parallelto the axes of said shafts; said rotors having a plurality of radialgear portions integrally formed therewith; pistons fitting boresdisposed uniformly therein and having engaging spur slidablywithin .saidbores and having rounded heads of reduced diameter extending outwardlyof said rotor sidesaid bores. r

4. A radial piston pump, comprising: a fluid' tight hous-v ing; a pairof stationary shafts disposed in axially parallel relationshipinteriorly of said housing; said shafts having fluid ducts therein, saidducts being apertured laterally of said shafts at one end and openingoutwardly of said housing at the other end; a pair of cylindrical rotorsjournalled "onsaid shafts, each of said rotors having a plurality ofradial bores disposed uniformly therein opening inwardly in alignmentwith said apertures of said ducts; pistons fitting slidably within saidbores and being provided With rounded heads of diminished -diameternormally extended outwardly of thecylindrical sidewalls of said rotors;said stationary shafts being spacedapart so as to bring the cylindricalsidewallsof said rotors into tangential rolling contact 'between saidparallel shafts; spring mea'ns'disposed in said bores being adapted tourge said pistons outwardly thereof; a piston retaining cylindricalband, perforated to receive said pistontheads of diminished di-'anieter, extending around the sidewall of each of said rotors'andeffective to-hold said pistons in said bores;

said rotors having engaging spur gear portions and power coupling meanseffective to counter-rotate 'said rotors 'whereby the pistons of eachare alternately depressed inwardly of said bores upon rotating intocontact'with said piston retaining band of the'othen p v 5. A radialpiston pump, comprising:' a fluid tight housing; a pair of stationaryshafts disposed in axially parallel relationship interiorly of saidhousing; said shafts having fluid ducts therein, one end of said ductsbeing terminated in apertures opening laterally of said shafts, theother ends'opening outwardly of said housing; a pair of cylindricalrotors journalled on said shafts, each of said'r'otors being integrallyformed with a spur gear portion and having a plurality of radial boresdisposed uniformly therein and opening inwardly in alignment with i saidlaterally opening apertures-of said ducts; pistons 1 fitting'slidablywithin said bores and being provided with rounded heads normallyextended outwardly of the cylindrical sidewalls of said rotors; saidstationary shafts being spaced apart so as to bring the cylindricalsidewalls of said rotors together in rollinglcontaet between saidparallel shafts and align saidfspur geanportions thereof revolveoppositely an'd the pistons of each of said rotors t are alternatelydepressed inwardly of said bores upon rotating intoiabutting contactwith said cylindrical sidewall of the other each piston beingreciprocated during rotation of the rotors through an arc of less thanfortyfive degrees. a 7

6. An opposed rotor radial piston pump, comprising a fluid tighthousing: a pair of stationary shafts disposed f 'axially parallelto eachother interiorly of said housing;

,pistons fitting slidably within said bores and being provided withrounded heads of diminished diameter normal-t 1y extended outwardly ofthe cylindrical sidewalls of inrrneshing engagement wherebys'aid rotorsare oaused'to revolve oppositely and the pistons of each of said rotors1 are alternately depressed inwardly of said bores upon rotating intoabutting contact with said piston retaining band of the other, therebydischarging through one of said ducts any fluid received in said boresfrom another of said ducts. V v

7. The invention in accordance with claim 6 being further characterizedby piston stress relieving means, comprising: said piston retainingbands being provided with shallow sockets disposed inwardly from theouter periphery of said bands and spaced intermediate of said pistonheads extended therethrough; said'sockets being complementary inconformation tosaid piston heads and adapted to receive said headsmovably therein.

8. A radial piston pump, comprising: a fluid-tight housing having fluidinlet and outlet apertures therein; a pair-of generally cylindricalrotors being tangentially disposed interiorly of said hou sing and beingjournalled on parallel shafts rigid with said housing; a plurality ofradial bores uniformly'disposed in each of said rotors; pistons slidableradially within said bores, and resilient spring means disposed inwardlyof said pistons in said -bores adapted to normally support said pistonswith their heads extended outwardly of said bores; gear means and powercoupling means being effective to contra-r0 tate said rotors; saidshaftsrdefining ported pintles having axial ducts therein communicatingwith said inlet and outlet apertures in said housing, and openinglaterally and oppositely of said pintles so as to communicate with saidradial bores in said rotors. I V t i 9. A radial piston pump inaccordance with claim 8 being further characterized by the amount ofnormal extension of said pistons outwardly of the circumference of saidrotors being adapted in length relative to the space provided by the.combined angleformed by the arcs of thetwo rotors adjacent their pointof tangency whereby the complete depression of a piston into a bore inone rotor, upon rotating into abutting contact with the peripheralsurface of the other rotor, is effected during rotational movement ofthe rotors of not.more than one-sixteenth of a complete revolution, thepistons of either rotor being depressed singly, and the pistons of bothrotors being depressed in alternate succession. '10. A radial pistonpump including the combination of: a pairrof cylindrical rotorsjournalled on parallel stationary shafts spaced apart so that thecylindrical surfaces of the rotors are intangential'rolling contact; aplurality of radial bores in at least one of said rotors; pistonsslidably disposed in said bores and having heads normally extendedoutwardly of the cylindrical surfaces of. the rotors; outwardly openingducts disposed axially in at least one of said shafts and aperturedlaterally thereof so as to communicate with said bores in'said rotors;gear and power coupling means effective to counterrotate the rptors andmove the heads of'the pistons 'outwardly of the rotors by centrifugalforce, the pistons in either rotor being reciprocated as their outwardlyextended heads rotate into contact with the cylindrical slidablydisposed in said bores and having heads normally extended outwardly ofthe cylindrical surfaces of the rotors; outwardly opening ducts disposedaxially in said shafts and apertured laterally thereof so as tocommunicate with the radial bores in the rotors; gear and power couplingmeans effective to counter-rotate the rotors and move the heads of thepistons outwardly of the rotors by centrifugal force, the pistons ineither rotor being reciprocated by reason of their outwardly extendedheads coming into contact with the cylindrical surface of the otherrotor, each piston being reciprocated during movement of the rotorsthrough an arc of less than forty-five degrees and being outwardlyextended during the balance of each revolution of the rotors.

12. A radial piston pump including the combination of claim 11 andwherein said radial bores and pistons therein are spaced apart by thesame distance on the cylindrical surface of each of said rotors.

13. A radial piston pump including the combination of: a pair ofcylindrical rotors, each having an axial aperture therethrough and aplurality of radial bores therein communicating between the cylindricalsidewalls and the axial apertures; said radial bores being spaced apartby the same distance on the cylindrical sidewalls of both of saidrotors; pistons slidably disposed in said radial bores and havingarcuate heads normally disposed outwardly of the cylindrical sidewallsof the rotors; said rotors being journalled on axially parallelstationary shafts; inlet and exhaust ducts extending axially in andopening laterally of said shafts, said inlet ducts being adapted tocommunicate with a majority of said bores and said exhaust ducts beingadapted to communicate with only one of said bores in each of saidrotors at a time; said axially parallel shafts being spaced apart so asto bring the cylindrical sidewalls into substantial tangential rollingcontact; said rotors being relatively positioned for rotation on saidshafts so that their radial bores and pistons therein occur alternatelyat the point of tangential rolling contact of the rotors; power couplingand gear means effective to counter rotate the rotors and to maintaintheir rotational relationship whereby each rotor is effective toreciprocate the pistons of the other rotor upon successive rotationalcontact with the outwardly disposed heads thereof.

14. In combination, a radial piston pump in accordance with claim 11 andpiston return springs adapted to move said pistons outwardly in saidbores only as far as necessary to draw the available inlet fluid intosaid bores, whereby reducing the fluid inlet fiow is efifective toshorten the stroke of said pistons and thereby reduce the volume offluid output without reducing its pressure.

References Cited in the file of this patent UNITED STATES PATENTS573,580 Dyer Dec. 22, 1896 683,834 Beckfield Oct. 1, 1901 868,100Krehbiel Oct. 15, 1907 1,817,370 Hammerstrorn Aug. 4, 1931 1,948,907Egli Feb. 27, 1934 1,978,441 Suenson Oct. 30, 1934 2,044,867 WoodwardJune 23, 1936 2,096,907 Linderman Oct. 26, 1937 2,504,841 Jones Apr. 18,1950 2,581,764 Leibing Jan. 8, 1952 2,612,110 Delegard Sept. 30, 19522,764,941 Miller et a1. Oct. 2, 1956 FOREIGN PATENTS 2,444 Great BritainFeb. 4, 1908 4,266 Great Britain Feb. 2, 1893 113,021 Switzerland Dec.16, 1925 422,312 Italy June 13, 1947 734,001 Germany Mar. 11, 1943

